This invention relates to compression release engine brakes, and more particularly to selectively reducing the engine exhaust noise associated with the use of such engine brakes.
Compression release engine brakes for internal combustion engines are well known as shown, for example, by Cummins U.S. Pat. No. 3,220,392. Such engine brakes typically operate by using an appropriately timed mechanical motion in one part of the associated internal combustion engine to open an exhaust valve in an engine cylinder whose piston is near top dead center of its compression stroke while the fuel supply to the engine is cut off. Opening the exhaust valve in this way allows the gas (air) that the piston has compressed to escape into the exhaust manifold of the engine. This prevents the engine from recovering the work of compressing that gas during the subsequent "power" stroke of the piston. In effect, the engine brake temporarily converts the engine from a power source to a power-sinking gas compressor. The engine can thus absorb more of the kinetic energy of the engine and the vehicle powered by that engine, thereby helping to slow down the vehicle. This conserves use of the vehicle's conventional wheel brakes, which prolongs the life of the wheel brakes and increases the safety of operation of the vehicle.
The abrupt opening of the engine exhaust valves produced by the engine brake while the gas in the associated engine cylinders is highly compressed tends to produce a relatively loud, staccato, "popping" sound in the engine's exhaust system. The amplitude of this sound may be almost as great as the "roar" of the engine exhaust when the engine is at full throttle in powering mode. In addition to being thus quite loud, the rapid, more discrete "pops" of the exhaust noise caused by operation of the engine brake may make that noise more annoying than the steadier roar of power mode engine exhaust. Neither of these kinds of exhaust noise may be particularly troublesome on the open road, but there are areas in which they may be objectionable to some people. For example, some urban areas have attempted to regulate or even preclude the use of compression release engine brakes because of objections to the engine exhaust noise they cause.
In view of the foregoing, it is an object of this invention to reduce the engine exhaust noise associated with the use of compression release engine brakes.
It is another object of this invention to provide a compression release engine brake that can be switched to a substantially quieter, but still effective mode of operation when desired.